The present invention relates generally to pumping devices, and more particularly to a fluid pump, such as a microscale fluid pump, using a temperature gradient across a multiple fluid interface to generate fluid motion.
It is well known to utilize microscale fluid pumps in various applications. The term xe2x80x9cmicroscalexe2x80x9d as used herein refers to an apparatus or method using a minimum amount of fluid to effectively perform a function. Many microscale pumps incorporate thermal technology, whereby heat is used to move the fluid. For example in a bubble jet printer, the fluid in a channel is heated to a boil to create a bubble until the pressure ejects a droplet of the fluid out of a nozzle. The bubble then collapses as the heating element cools, and the resulting vacuum draws fluid from a reservoir to replace the fluid that was ejected from the channel. Thermal technology requires that the fluid to be pumped be resistant to heat, i.e. capable of being boiled without significant breakdown. Also, the need for a cooling period between ejecting successive droplets from a nozzle places speed limitations on thermal microscale pumps.
Piezoelectric microscale pumps, such as that disclosed in U.S. Pat. No. 5,224,843, have a piezoelectric crystal in the fluid channel that flexes when an electric current flows through it to force a drop of fluid out of a nozzle. Piezoelectric technology is faster and provides more control over the fluid movement as compared to thermal technology. Also, because the fluid to be pumped is not heated significantly, the fluid can be selected based on its relevant properties rather than its ability to withstand high temperatures. However, piezoelectric microscale pumps are complex and thus expensive to manufacture. U.S. Pat. Nos. 5,362,213 and 5,499,409 disclose microscale pumps having movable parts. Such pumps are relatively complex and required high maintenance.
Further, microscale fluid pumps find use in various other applications in which a high degree of control is required and high temperatures are to be avoided. For example, microscale fluid pumps can be used in biological heat-pipe type devices, devices which administer small doses of fluid into a larger stream of fluid, devices which pump various solutions that are unstable when boiled, devices which pump biological materials and other materials that must be maintained at a constant temperature, and other generic pumping applications. Accordingly, there is a need for a microscale fluid pump that is simple in construction and capable of pumping fluid quickly and accurately without boiling the fluid.
An object of the invention is to increase the control accuracy of microscale fluid pumps.
Another object of the invention is to simplify the construction of microscale fluid pumps.
Another object of the invention is to impart motion to fluid without the need for moving parts or boiling of the fluid.
Another object of the invention is to utilize standard CMOS processes to manufacture a microscale fluid pump.
Another object of the invention is to reduce the power required by microscale fluid pumps.
The invention achieves these and other objects through a first aspect of the invention which is a fluid pump comprising a body, a primary fluid channel defined in the body, a primary fluid supply coupled to the primary fluid channel to supply a primary fluid to the primary fluid channel, a mechanism for introducing a secondary fluid to an interface region of the primary fluid channel to thereby define a fluid interface between the primary fluid and the secondary fluid in the interface region, and an energy delivery device disposed proximate the interface region to selectively create a temperature gradient along the fluid interface to thereby impart motion to the primary fluid.
A second aspect of the invention is a method for pumping fluid comprising the steps of supplying a primary fluid to a primary fluid channel formed in a body, introducing a secondary fluid to an interface region of the primary fluid channel to define a fluid interface between the primary fluid and the secondary fluid in the interface region, and delivering energy to the interface region to create a temperature gradient along the fluid interface and impart motion to the primary fluid.